Remotely sensed canopy nitrogen correlates with nitrous oxide emissions in a lowland tropical rainforest

Abstract

Tropical forests exhibit significant heterogeneity in plant functional and chemical traits that may contribute to spatial patterns of key soil biogeochemical processes, such as carbon storage and greenhouse gas emissions. Although tropical forests are the largest ecosystem source of nitrous oxide (N O), drivers of spatial patterns within forests are poorly resolved. Here, we show that local variation in canopy foliar N, mapped by remote-sensing image spectroscopy, correlates with patterns of soil N O emission from a lowland tropical rainforest. We identified ten 0.25 ha plots (assemblages of 40-70 individual trees) in which average remotely-sensed canopy N fell above or below the regional mean. The plots were located on a single minimally-dissected terrace (<1 km ) where soil type, vegetation structure and climatic conditions were relatively constant. We measured N O fluxes monthly for 1 yr and found that high canopy N species assemblages had on average three-fold higher total mean N O fluxes than nearby lower canopy N areas. These differences are consistent with strong differences in litter stoichiometry, nitrification rates and soil nitrate concentrations. Canopy N status was also associated with microbial community characteristics: lower canopy N plots had two-fold greater soil fungal to bacterial ratios and a significantly lower abundance of ammonia-oxidizing archaea, although genes associated with denitrification (nirS, nirK, nosZ) showed no relationship with N O flux. Overall, landscape emissions from this ecosystem are at the lowest end of the spectrum reported for tropical forests, consist with multiple metrics indicating that these highly productive forests retain N tightly and have low plant-available losses. These data point to connections between canopy and soil processes that have largely been overlooked as a driver of denitrification. Defining relationships between remotely-sensed plant traits and soil processes offers the chance to map these processes at large scales, potentially increasing our ability to predict N O emissions in heterogeneous landscapes.

Biogeochemical recuperation of lowland tropical forest during succession

“…For example, the decline in litter mass : N during secondary succession is consistent with the notion that plants may resorb less N prior to abscission late in succession than early in succession, before N capital has been restored by N 2 fixation (Batterman et al 2013). Plant traits such as litter chemistry can shape local biogeochemical cycling rates by influencing processes including decomposition and mineralization (Osborne et al 2017, Soper et al 2018. Increasing foliar d 15 N during secondary succession could be the product of numerous processes, but is consistent with fractionation of the soil N pool associated with increased soil N gas loss (Houlton et al 2006), as we observed, and with declining symbiotic N 2 fixation inputs during secondary succession (Barron et al 2011, Batterman et al 2013, Sullivan et al 2014) that may be associated with down-regulation of N 2 fixation in facultative species with increasing soil N availability.…”

“…A recent model analysis demonstrated that the resilience of tropical forest to climate-change type disturbance may depend on plant trait diversity (Sakschewski et al 2016), which could reflect the influence of plant traits on biogeochemical cycling (Soper et al 2018). A recent model analysis demonstrated that the resilience of tropical forest to climate-change type disturbance may depend on plant trait diversity (Sakschewski et al 2016), which could reflect the influence of plant traits on biogeochemical cycling (Soper et al 2018).…”

“…As community composition transitions toward that of a mature forest during secondary succession (Peña-Claros 2003, Chazdon 2014, plant nutrient acquisition strategies may also shift to favor new biogeochemical conditions, such as a more NO À 3 -dominated N cycle. Plant traits such as litter chemistry can shape local biogeochemical cycling rates by influencing processes including decomposition and mineralization (Osborne et al 2017, Soper et al 2018. Plant traits such as litter chemistry can shape local biogeochemical cycling rates by influencing processes including decomposition and mineralization (Osborne et al 2017, Soper et al 2018.…”

“…Shifts in plant community composition during succession are likely both a response to, and a cause of, concurrent changes in soil nutrient availability. A recent model analysis demonstrated that the resilience of tropical forest to climate-change type disturbance may depend on plant trait diversity (Sakschewski et al 2016), which could reflect the influence of plant traits on biogeochemical cycling (Soper et al 2018). As community composition transitions toward that of a mature forest during secondary succession (Peña-Claros 2003, Chazdon 2014, plant nutrient acquisition strategies may also shift to favor new biogeochemical conditions, such as a more NO À 3 -dominated N cycle.…”

Plant trait‐based approaches to improve nitrogen cycling in agroecosystems

“…F I G U R E 4 Methodological and interdisciplinary approaches needed to explore the plant functional traits that determine N-cycling and NUE in intensive agroecosystems For example, a combination of remote sensing (e.g. Unmanned Aerial Vehicles) and imaging spectroscopy enables for non-invasive assessment of plant traits such as LNC (Soper et al, 2018;van der Meij, Kooistra, Suomalainen, Barel, & De Deyn, 2017), essential for estimation of NUE at enhanced spatial-temporal resolutions. Process-based biogeochemical models (e.g.…”